The Dynamics of Known Centaurs

We have numerically investigated the long term dynamical behavior of known Centaurs. This class of objects is thought to constitute the transitional population between the Kuiper Belt and the Jupiter-family comets (JFCs). In our study, we find that this transient population diffuses into the JFCs and other sinks, but (not surprisingly) does not diffuse back into the parameter space representing the presumed Kuiper Belt source. Their orbital evolution is characterized by frequent close encounters with the giant planets. Most of these Centaurs will escape from the solar system (or enter the Oort Cloud), while a fraction will enter the JFC population and a few percent will impact a giant planet. Their median dynamical lifetime is 9 Myr, although there is a wide dispersion in lifetimes, ranging from less than 1 Myr to more than 100 Myr. We find the dynamical evolution of this sample of Centaurs to be less orderly than the planet-toplanet “hand-off” described in previous investigations. Based on our simulations, and assuming a steady-state population, we estimate the spatial distribution of Centaurs: their surface density increases steeply from r = 5 AU to about r = 15 AU, is nearly constant from r = 15 AU to r = 30 AU, peaks near 30 AU, and decreases thereafter approximately as a power law, ∼ r, where r is heliocentric distance.